Consumerresource Interactions Chapter 17

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Consumer-resource Interactions (Chapter 17)

• Overview of community interactions
• Predator-prey relationships
• Host-parasite relationships
• Herbivore-plant relationships

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Types of consumer-resource interactions
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• Predator a heterotroph (usually an animal) that
  kills and eats living organisms for food

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• Characteristics of predators
• Size of prey is proportional to size of predator
• large prey can be dangerous
• small prey dont provide enough energy

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• Cooperative hunting
• allows larger prey to be taken
• Ability to tear skin and flesh
• sharp teeth
• hooked beaks and claws
• jaws that open very widely

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• Tactics to Avoid Being Eaten
• Escape
• early detection of predators
• speed
• Hiding
• stay near cover
• reducing activity
• Physical defenses
• armor
• horns, antlers, claws, teeth, etc.
• large body size

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• Crypsis avoiding detection by matching the
  color or pattern of the background

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• Chemical defenses
• noxious sprays
• poisonous chemicals in body tissues
• often accompanied by aposematic (bright,
  contrasting) warning coloration

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• Mimicry
• Batesian mimicry a palatable or harmless
  organism appears similar to an unpalatable or
  harmful organism
• Associated with aposematic colors

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• Müllerian mimicry when unpalatable species
  evolve to resemble one another
• creates more opportunities for predators to learn
  to avoid them

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• Large groups
• increased detection of predators
• decreased odds that any individual is eaten
• Predator satiation
• overwhelming predator populations by producing
  many, many seeds or young at irregular intervals
• masting synchronous, widespread seed production

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• Parasite-host Relationships
• Parasite consumes part of a living prey
  organism (host)
• can be internal or external
• do not directly kill the host
• Parasitoid animals that lay eggs on living
  organisms and whose larvae eat and kill the host
• usually flies and wasps

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• Parasites can have complex life cycles

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• Virulence the ability of a parasite to do harm
  to its host
• For parasites, there is a tradeoff
• too little virulence parasite is unable to
  survive, reproduce
• too much virulence parasite kills its host and
  cannot reproduce
• Most parasites have low virulence

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• Herbivores eat whole plants or parts of plants.
• Grazing eating grasses, herbaceous vegetation,
  or algae
• Browsing eating woody vegetation

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• Herbivore impacts on plant communities
• Herbivores can dramatically reduce plant
  populations
• grasslands herbivores consume 30-60 of
  above-ground vegetation
• forests herbivores consume 10 of veg.
• Some plants are adapted to be grazed

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• Adaptations of herbivores
• Teeth with large grinding surfaces or cutting
  surfaces
• Long guts
• Stomach with fermentation chambers

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• Plant defense against herbivory
• Low nutritional value of plant tissues
• Toxic compounds
• Structural defenses
• spines
• hairs
• hard shells on seeds
• sticky gums and resins

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• Chemical Defenses of Plants
• Secondary compounds chemicals made by plants to
  defend themselves against herbivores
• tannins bitter-tasting chemicals that inhibit
  digestion of proteins
• Can have a variety of toxic effects on herbivores
• Herbivores often evolve resistance to secondary
  compound

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• Chemical defenses can be
• constitutive maintained at all times, or
• induced manufactured in response to herbivore
  damage

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